When the strict level is zero and BUG_ON() is not implemented, some
possible null-deref warnings are emitted again because some were
covering for these cases. Let's make it fall back to ASSUME() so that
the compiler continues to know that the tested expression never happens.
It also allows to further optimize certain functions by helping the
compiler eliminate certain tests for impossible values. However it
requires that the expression is really evaluated before passing the
result through ASSUME() otherwise it was shown that gcc-11 and above
will fail to evaluate its implications and will continue to emit the
null-deref warnings in case the expression is non-trivial (e.g. it
has multiple terms).
We don't do it for BUG_ON_HOT() however because the extra cost of
evaluating the condition is generally not welcome in fast paths,
particularly when that BUG_ON_HOT() was kept disabled for
performance reasons.
Commit 7f64bb79fd ("BUG/MINOR: debug: COUNT_IF() should return true/false")
allowed the COUNT_IF() macro to return the evaluated value. This is handy
to place it in "if ()" conditions and count them at the same time. When
glitches are disabled, the condition is just returned as-is, but most call
places do not use the result, making some compilers complain. In addition,
while reviewing this, it was noticed that when DEBUG_STRICT=0, the macro
would still be replaced by a "do { } while (0)" statement, which not only
does not evaluate the expression, but also cannot return anything. Ditto
for COUNT_IF_HOT().
Let's make sure both are always properly evaluated now.
The COUNT_IF() macro was initially meant to return true/false to be used
in if() conditions but had an extra do { } while(0) that prevents it from
doing so. Let's get rid of the do { } while(0) before the code generalizes
to too many places. There's no impact on existing code, but may have to be
backported if future fixes rely on it.
COUNT_GLITCH() will implement an unconditional counter on its declaration
line when DEBUG_GLITCHES is set, and do nothing otherwise. The output will
be reported as "GLT" and can be filtered as "glt" on the CLI. The purpose
is to help figure what's happening if some glitches counters start going
through the roof. The macro supports an optional string argument to
describe the cause of the glitch (e.g. "truncated header"), which is then
reported in the dump.
For now this is conditioned by DEBUG_GLITCHES but if it turns out to be
light enough, maybe we'll keep it enabled full time. In this case it
might have to be moved away from debug dev, or at least documented (or
done as debug counters maybe so that dev can remain undocumented and
updatable within a branch?).
In order to count new event types, we'll need to support empty conditions
so that we don't have to fake if (1) that would pollute the output. This
change checks if #cond is an empty string before concatenating it with
the optional var args, and avoids dumping the colon on the dump if the
whole description is empty.
In order to help users detect when threads are behaving abnormally, let's
try to emit a warning when one is no longer making any progress. This will
allow to catch faulty situations more accurately, instead of occasionally
triggering just after the long task. It will also let users know that there
is something wrong with their configuration, and inspect the call trace to
figure whether they're using excessively long rules or Lua for example (the
usual warnings about lua-load vs lua-load-per-thread are still reported).
The warning will only be emitted for threads not yet marked as stuck so
as not to interfere with panic dumps and avoid sending a warning just
before a panic. A tainted flag is set when this happens however (0x2000).
This macro works exactly like BUG_ON() except that it never logs anything
nor crashes, it only implements an atomic counter that is incremented on
every call. This can be used to count a number of unlikely events that are
worth checking at run time on setups showing unusual and unreproducible
behaviors.
These macros do not always kill the process, and sometimes it would be
nice to know if some match or not, and how many times (especially for the
CHECK_IF one).
This commit adds a new section "dbg_cnt" made of structs that contain
function name, file name, line number, check type, condition and match
count. A newe macro __DBG_COUNT() adds one to the counter, and is placed
inside _BUG_ON() and _BUG_ON_ONCE(). It's worth noting that the exact
type of the check is not very precise but in practice we don't care,
as most checks will cause the process to die anyway unless they're of
type _BUG_ON_ONCE() (used by CHECK_IF by default).
All of this is limited to !defined(USE_OBSOLETE_LINKER) because we're
creating a section, thus we need a modern linker to be able to scan
this section later. Doing so adds ~50kB to the executable due to the
~1266 BUG_ON() and others placed there. That's not huge in comparison
to the visibility it can provide.
The BUG_ON() macros are made of two levels so as to resolve the condition
to a string. However this doesn't offer much flexibility for performing
other operations when the condition is validated, so let's adjust them so
that the condition is checked in the outer macro and the operations are
performed in the inner one.
Since mark_tainted() uses atomic ops to update the tainted status, let's
make it return the prior value, which will allow the caller to detect
if it's the first one to set it or not.
Compilation issue detected as follows by gcc:
In file included from src/ncbuf.c:19:
src/ncbuf.c: In function 'ncb_write_off':
include/haproxy/bug.h:144:10: error: unknown type name 'ssize_t'
144 | extern ssize_t write(int, const void *, size_t); \
Previous commit 8f204fa8ae ("MINOR: debug: print gdb hints when crashing")
broken on the CI where strlen() isn't known. Let's forward-declare it in
the __ABORT_NOW() functions, just like write(). No backport is needed.
To make bug reporting easier for users, when crashing, let's suggest
what to do. Typically when a BUG_ON() matches, only the current thread
is useful the vast majority of the time, while when the watchdog
triggers, all threads are interesting.
The messages are printed at the end after the dump. We may adjust these
with wiki links in the future is more detailed instructions are relevant.
Setting DEBUG_STRICT=0 only validates the defined(DEBUG_STRICT) test
regarding DEBUG_STRICT_ACTION, which is equivalent to DEBUG_STRICT>=0.
Let's make sure the test checks for >0 so that DEBUG_STRICT=0 properly
disables DEBUG_STRICT.
Some include files, mostly types definitions, are missing a few includes
to define the types they're using, causing include ordering dependencies
between files, which are most often not seen due to the alphabetical
order of includes. Let's just fix them.
These were spotted by building pre-compiled headers for all these files
to .h.gch.
This commit adds support for an optional second argument to BUG_ON(),
WARN_ON(), CHECK_IF(), that can be a constant string. When such an
argument is given, it will be printed on a second line after the
existing first message that contains the condition.
This can be used to provide more human-readable explanations about
what happened, such as "too low on memory" or "memory corruption
detected" that may help a user resolve the incident by themselves.
The ABORT_NOW() macro is not much used since we have BUG_ON(), but
there are situations where it makes sense, typically if the program
must always die regardless od DEBUG_STRICT, or if the condition must
always be evaluated (e.g. decompress something and check it).
It's not convenient not to have any hint about what happened there. But
providing too much info also results in wiping some registers, making
the trace less exploitable, so a compromise must be found.
What this patch does is to provide the support for an optional argument
to ABORT_NOW(). When an argument is passed (a string), then a message
will be emitted with the file name, line number, the message and a
trailing LF, before the stack dump and the crash. It should be used
reasonably, for example in functions that have multiple calls that need
to be more easily distinguished.
As seen in previous commit 59acb27001 ("BUILD: quic: Variable name typo
inside a BUG_ON()."), it can sometimes happen that with DEBUG forced
without DEBUG_STRICT, BUG_ON() statements are ignored. Sadly, it means
that typos there are not even build-tested.
This patch makes these statements reference sizeof(cond) to make sure
the condition is parsed. This doesn't result in any code being emitted,
but makes sure the expression is correct so that an issue such as the one
above will fail to build (which was verified).
This may be backported as it can help spot failed backports as well.
Since d480b7b ("MINOR: debug: make ABORT_NOW() store the caller's line
number when using abort"), building with 'DEBUG_USE_ABORT' fails with:
|In file included from include/haproxy/api.h:35,
| from include/haproxy/activity.h:26,
| from src/ev_poll.c:20:
|include/haproxy/thread.h: In function ‘ha_set_thread’:
|include/haproxy/bug.h:107:47: error: expected ‘;’ before ‘_with_line’
| 107 | #define ABORT_NOW() do { DUMP_TRACE(); abort()_with_line(__LINE__); } while (0)
| | ^~~~~~~~~~
|include/haproxy/bug.h:129:25: note: in expansion of macro ‘ABORT_NOW’
| 129 | ABORT_NOW(); \
| | ^~~~~~~~~
|include/haproxy/bug.h:123:9: note: in expansion of macro ‘__BUG_ON’
| 123 | __BUG_ON(cond, file, line, crash, pfx, sfx)
| | ^~~~~~~~
|include/haproxy/bug.h:174:30: note: in expansion of macro ‘_BUG_ON’
| 174 | # define BUG_ON(cond) _BUG_ON (cond, __FILE__, __LINE__, 3, "FATAL: bug ", "")
| | ^~~~~~~
|include/haproxy/thread.h:201:17: note: in expansion of macro ‘BUG_ON’
| 201 | BUG_ON(!thr->ltid_bit);
| | ^~~~~~
|compilation terminated due to -Wfatal-errors.
|make: *** [Makefile:1006: src/ev_poll.o] Error 1
This is because of a leftover: abort()_with_line(__LINE__);
^^
Fixing it by removing the extra parentheses after 'abort' since the
abort() call is now performed under abort_with_line() helper function.
This was raised by Ilya in GH #2440.
No backport is needed, unless the above commit gets backported.
Placing DO_NOT_FOLD() before abort() only works in -O2 but not in -Os which
continues to place only 5 calls to abort() in h3.o for call places. The
approach taken here is to replace abort() with a new function that wraps
it and stores the line number in the stack. This slightly increases the
code size (+0.1%) but when unwinding a crash, the line number remains
present now. This is a very low cost, especially if we consider that
DEBUG_USE_ABORT is almost only used by code coverage tools and occasional
debugging sessions.
As indicated in previous commit, we don't want calls to ha_crash_now()
to be merged, since it will make gdb return a wrong line number. This
was found to happen with gcc 4.7 and 4.8 in h3.c where 26 calls end up
as only 5 to 18 "ud2" instructions depending on optimizations. By
calling DO_NOT_FOLD() just before provoking the trap, we can reliably
avoid this folding problem. Note that this does not address the case
where abort() is used instead (DEBUG_USE_ABORT).
Now when calling ha_panic() with a thread still under malloc_trim(),
we'll set a new tainted flag to easily report it, and the output
trace will report that this condition happened and will suggest to
use no-memory-trimming to avoid it in the future.
William suggested that since we can detect the presence of Lua in the
stack, let's combine it with stuck detection to set a new pair of flags
indicating a stuck Lua context and a stuck Lua shared context.
Now, executing an infinite loop in a Lua sample fetch function with
yield disabled crashes with tainted=0xe40 if loaded from a lua-load
statement, or tainted=0x640 from a lua-load-per-thread statement.
In addition, at the end of the panic dump, we can check if Lua was
seen stuck and emit recommendations about lua-load-per-thread and
the choice of dependencies depending on the presence of threads
and/or shared context.
This will make it easier to know that the panic function was called,
for the occasional case where the dump crashes and/or the stack is
corrupted and not much exploitable. Now at least it will be sufficient
to check the tainted value to know that someone called ha_panic(), and
it will also be usable to condition extra analysis.
When building without threads, the recently introduced BUG_ON(tid != 0)
turns to a constant expression that evaluates to 0 and that is not used,
resulting in this warning:
src/connection.c: In function 'conn_free':
src/connection.c:584:3: warning: statement with no effect [-Wunused-value]
This is because the whole thing is declared as an expression for clarity.
Make it return void to avoid this. No backport is needed.
On aarch64 there's also a guaranted invalid instruction, called UDF, and
which even supports an optional 16-bit immediate operand:
https://developer.arm.com/documentation/ddi0596/2021-12/Base-Instructions/UDF--Permanently-Undefined-?lang=en
It's conveniently encoded as 4 zeroes (when the operand is zero). It's
unclear when support for it was added into GAS, if at all; even a
not-so-old 2.27 doesn't know about it. Let's byte-encode it.
Tested on an A72 and works as expected.
BUG_ON() calls currently trigger a segfault. This is more convenient
than abort() as it doesn't rely on any function call nor signal handler
and never causes non-unwindable stacks when opening cores. But it adds
quite some confusion in bug reports which are rightfully tagged "segv"
and do not instantly allow to distinguish real segv (e.g. null derefs)
from code asserts.
Some CPU architectures offer various crashing methods. On x86 we have
INT3 (0xCC), which stops into the debugger, and UD0/UD1/UD2. INT3 looks
appealing but for whatever reason (maybe signal handling somewhere) it
loses the last call point in the stack, making backtraces unusable. UD2
has the merit of being only 2 bytes and causing an invalid instruction,
which almost never happens normally, so it's easily distinguishable.
Here it was defined as a macro so that the line number in the core
matches the one where the BUG_ON() macro is called, and the debugger
shows the last frame exactly at its calligg point.
E.g. when calling "debug dev bug":
Program terminated with signal SIGILL, Illegal instruction.
#0 debug_parse_cli_bug (args=<optimized out>, payload=<optimized out>, appctx=<optimized out>, private=<optimized out>) at src/debug.c:408
408 BUG_ON(one > zero);
[Current thread is 1 (Thread 0x7f7a660cc1c0 (LWP 14238))]
(gdb) bt
#0 debug_parse_cli_bug (args=<optimized out>, payload=<optimized out>, appctx=<optimized out>, private=<optimized out>) at src/debug.c:408
#1 debug_parse_cli_bug (args=<optimized out>, payload=<optimized out>, appctx=<optimized out>, private=<optimized out>) at src/debug.c:402
#2 0x000000000061a69f in cli_parse_request (appctx=appctx@entry=0x181c0160) at src/cli.c:832
#3 0x000000000061af86 in cli_io_handler (appctx=0x181c0160) at src/cli.c:1035
#4 0x00000000006ca2f2 in task_run_applet (t=0x181c0290, context=0x181c0160, state=<optimized out>) at src/applet.c:449
Once in a while we introduce an sprintf() or strncat() function by
accident. These ones are particularly dangerous and must never ever
be used because the only way to use them safely is at least as
complicated if not more, than their safe counterparts. By redefining
a few of these functions with an attribute_warning() we can deliver a
message to the developer who is tempted to use them. This commit does
it for strcat(), strcpy(), strncat(), sprintf(), vsprintf(). More could
come later if needed, such as strtok() and maybe a few others, but these
are less common.
Instead of reporting the inaccurate "malloc_trim() support" on -vv, let's
report the case where the memory allocator was actively replaced from the
one used at build time, as this is the corner case we want to be cautious
about. We also put a tainted bit when this happens so that it's possible
to detect it at run time (e.g. the user might have inherited it from an
environment variable during a reload operation).
The now unused is_trim_enabled() function was finally dropped.
HA_WEAK() is supposed to take a symbol in argument, not a string, since
the asm statements it produces already quote the argument. Having it
quoted twice doesn't work on older compilers and was the only reason
why DEBUG_MEM_STATS didn't work on older compilers.
The memstats code currently defines its own file/function/line number,
type and extra pointer. We don't need to keep them separate and we can
easily replace them all with just a struct ha_caller. Note that the
extra pointer could be converted to a pool ID stored into arg8 or
arg32 and be dropped as well, but this would first require to define
IDs for pools (which we currently do not have).
The purpose of this structure is to assemble all constant parts of a
generic calling point for a specific event. These ones are created by
the compiler as a static const element outside of the code path, so
they cost nothing in terms of CPU, and a pointer to that descriptor
can be passed to the place that needs it. This is very similar to what
is being done for the mem_stat stuff.
This will be useful to simplify and improve DEBUG_TASK.
As outlined in commit f7ebe584d7 ("BUILD: debug: Add braces to if
statement calling only CHECK_IF()"), the BUG_ON() family of macros
is incorrectly defined to be empty when debugging is disabled, and
that can lead to trouble. Make sure they always fall back to the
usual "do { } while (0)". This may be backported to 2.6 if needed,
though no such issue was met there to date.
Right now the free() call is not intercepted since all this is done
using macros and that would break a lot of stuff. Instead a __free()
macro was provided but never used. In addition it used to only report
a zero size, which is not very convenient.
With this patch comes a better solution. Instead it provides a new
will_free() macro that can be prepended before a call to free(). It
only keeps the counters up to date, and also supports being passed a
size. The pool_free_area() command now uses it, which finally allows
the stats to look correct:
pool-os.h:38 MALLOC size: 5802127832 calls: 3868044 size/call: 1500
pool-os.h:47 FREE size: 5800041576 calls: 3867444 size/call: 1499
The few other places directly calling free() could now be instrumented to
use this and to pass the correct sizeof() when known.
The calling function name is now stored in the structure, and it's
reported when the "all" argument is passed. The first column is
significantly enlarged because some names are really wide :-(
Not specifying the alignment will let the linker choose it, and it turns
out that it will not necessarily be the same size as the one chosen for
struct mem_stats, as can be seen if any new fields are added there. Let's
enforce an alignment to void* both for the section and for the structure.
In 2.6, 8a0fd3a36 ("BUILD: debug: work around gcc-12 excessive
-Warray-bounds warnings") disabled some warnings that were reported
around the the BUG() statement. But the -Wnull-dereference warning
isn't known from gcc-5, it only arrived in gcc-6, hence makes gcc-5
complain loudly that it doesn't know this directive. Let's just
condition this one to gcc-6.
Sometimes using "debug dev memstats" can be frustrating because all
pool allocations are reported through pool-os.h and that's all.
But in practice there's nothing wrong with also intercepting pool_alloc,
pool_free and pool_zalloc and report their call counts and locations,
so that's what this patch does. It only uses an alternate set of macroes
for these 3 calls when DEBUG_MEM_STATS is defined. The outputs are
reported as P_ALLOC (for both pool_malloc() and pool_zalloc()) and
P_FREE (for pool_free()).
In order to better detect the danger caused by extra shared libraries
which replace some symbols, upon dlopen() we now compare a few critical
symbols such as malloc(), free(), and some OpenSSL symbols, to see if
the loaded library comes with its own version. If this happens, a
warning is emitted and TAINTED_REDEFINITION is set. This is important
because some external libs might be linked against different libraries
than the ones haproxy was linked with, and most often this will end
very badly (e.g. an OpenSSL object is allocated by haproxy and freed
by such libs).
Since the main source of dlopen() calls is the Lua lib, via a "require"
statement, it's worth trying to show a Lua call trace when detecting a
symbol redefinition during dlopen(). As such we emit a Lua backtrace if
Lua is detected as being in use.
Several bug reports were caused by shared libraries being loaded by other
libraries or some Lua code. Such libraries could define alternate symbols
or include dependencies to alternate versions of a library used by haproxy,
making it very hard to understand backtraces and analyze the issue.
Let's intercept dlopen() and set a new TAINTED_SHARED_LIBS flag when it
succeeds, so that "show info" makes it visible that some external libs
were added.
The redefinition is based on the definition of RTLD_DEFAULT or RTLD_NEXT
that were previously used to detect that dlsym() is usable, since we need
it as well. This should be sufficient to catch most situations.
As was first reported by Ilya in issue #1513, compiling with gcc-12
adds warnings about size 0 around each BUG_ON() call due to the
ABORT_NOW() macro that tries to dereference pointer value 1.
The problem is known, seems to be complex inside gcc and could only
be worked around for now by adjusting a pointer limit so that the
warning still catches NULL derefs in the first page but not other
values commonly used in kernels and boot loaders:
https://gcc.gnu.org/git/gitweb.cgi?p=gcc.git;h=91f7d7e1b
It's described in more details here:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104657https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99578https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103768
And some projects had to work around it using various approaches,
some of which are described in the bugs reports above, plus another
one here:
https://mail.coreboot.org/hyperkitty/list/seabios@seabios.org/thread/HLK3BHP2T3FN6FZ46BIPIK3VD5FOU74Z/
In haproxy we can hide it by hiding the pointer in a DISGUISE() macro,
but this forces the pointer to be loaded into a register, so that
register is lost precisely where we want to get the maximum of them.
In our case we purposely use a low-value non-null pointer because:
- it's mandatory that this value fits within an unmapped page and
only the lowest one has this property
- we really want to avoid register loads for the address, as these
will be lost and will complicate the bug analysis, and they tend
to be used for large addresses (i.e. instruction length limit).
- the compiler may decide to optimize away the null deref when it
sees it (seen in the past already)
As such, the current workaround merged in gcc-12 is not effective for
us.
Another approach consists in using pragmas to silently disable
-Warray-bounds and -Wnull-dereference only for this part. The problem
is that pragmas cannot be placed into macros.
The resulting solution consists in defining a forced-inlined function
only to trigger the crash, and surround the dereference with pragmas,
themselves conditionned to gcc >= 5 since older versions don't
understand them (but they don't complain on the dereference at least).
This way the code remains the same even at -O0, without the stack
pointer being modified nor any address register being modified on
common archs (x86 at least). A variation could have been to rely on
__builtin_trap() but it's not everywhere and it behaves differently
on different platforms (undefined opcode or a nasty abort()) while
the segv remains uniform and effective.
This may need to be backported to older releases once users start to
complain about gcc-12 breakage.
While weak symbols were finally fixed with commit fb1b6f5bc ("BUILD:
compiler: use a more portable set of asm(".weak") statements"), it
was an error to think that initcall symbols were also weak. They must
not be and they're only global. The reason is that any externally
linked code loaded as a .so would drop its weak symbols when being
loaded, hence its initcalls that may contain various function
registration calls.
The ambiguity came from the fact that we initially reused the initcall's
HA_GLOBL macro for OSX then generalized it, then turned it to a choice
between .globl and .weak based on the OS, while in fact we needed a
macro to define weak symbols.
Let's rename the macro to HA_WEAK() to make it clear it's only for weak
symbols, and redefine HA_GLOBL() that initcall needs.
This will need to be backported wherever the commit above is backported
(at least 2.5 for now).
The two recent patches b12966af1 ("BUILD: debug: mark the
__start_mem_stats/__stop_mem_stats symbols as weak") and 2a06e248f
("BUILD: initcall: mark the __start_i_* symbols as weak, not global")
aimed at fixing a build warning and resulted in a build breakage on
MacOS which doesn't have a ".weak" asm statement.
We've already had MacOS-specific asm() statements for section names, so
this patch continues on this trend by moving HA_GLOBL() to compiler.h
and using ".globl" on MacOS since apparently nobody complains there.
It is debatable whether to expose this only when !USE_OBSOLETE_LINKER
or all the time, but since these are just macroes it's no big deal to
let them be available when needed and let the caller decide on the
build conditions.
If any of the patches above is backported, this one will need to as
well.
Building with clang and DEBUG_MEM_STATS shows the following warnings:
warning: __start_mem_stats changed binding to STB_WEAK [-Wsource-mgr]
warning: __stop_mem_stats changed binding to STB_WEAK [-Wsource-mgr]
The reason is that the symbols are declared using ".globl" while they
are also referenced as __attribute__((weak)) elsewhere. It turns out
that a weak symbol is implicitly a global one and that the two classes
are exclusive, thus it may confuse the linker. Better fix this.
This may be backported where the patch applies.
Many inline functions involve some BUG_ON() calls and because of the
partial complexity of the functions, they're not inlined anymore (e.g.
co_data()). The reason is that the expression instantiates the message,
its size, sometimes a counter, then the atomic OR to taint the process,
and the back trace. That can be a lot for an inline function and most
of it is always the same.
This commit modifies this by delegating the common parts to a dedicated
function "complain()" that takes care of updating the counter if needed,
writing the message and measuring its length, and tainting the process.
This way the caller only has to check a condition, pass a pointer to the
preset message, and the info about the type (bug or warn) for the tainting,
then decide whether to dump or crash. Note that this part could also be
moved to the function but resulted in complain() always being at the top
of the stack, which didn't seem like an improvement.
Thanks to these changes, the BUG_ON() calls do not result in uninlining
functions anymore and the overall code size was reduced by 60 to 120 kB
depending on the build options.
The new macro was introduced with commit 86bcc5308 ("DEBUG: implement 4
levels of choices between warn and crash.") but some older compilers can
complain that we test the value when the macro is not defined despite
having already been checked in a previous #if directive. Let's just
repeat the test for the definition.
Two new BUG_ON variants, BUG_ON_HOT() and CHECK_IF_HOT() are introduced
to debug hot paths (such as low-level API functions). These ones must
not be enabled by default as they would significantly affect performance
but they may be enabled by setting DEBUG_STRICT to a value above 1. In
this case, DEBUG_STRICT_ACTION is mostly respected with a small change,
which is that the no_crash variant of BUG_ON() isn't turned to a regular
warning but to a one-time warning so as not to spam with warnings in a
hot path. It is for this reason that there is no WARN_ON_HOT().
We used to have DEBUG_STRICT_NOCRASH to disable crashes on BUG_ON().
Now we have other levels (WARN_ON(), CHECK_IF()) so we need something
finer-grained.
This patch introduces DEBUG_STRICT_ACTION which takes an integer value.
0 disables crashes and is the equivalent of DEBUG_STRICT_NOCRASH. 1 is
the default and only enables crashes on BUG_ON(). 2 also enables crashes
on WARN_ON(), and 3 also enables warnings on CHECK_IF(), and is suited
to developers and CI.
Now we'll explicitly mention if the test was a bug/warn/check, and
"FATAL" is only displayed when the process crashes. The non-crashing
BUG_ON() also suggests to report to developers.
